9212: Crop and soil P-test responses to agronomic use of waste-derived phosphorus

Rubæk, Gitte; Frossard, Emmanuel and Christensen, Bent Tolstrup (2006) Crop and soil P-test responses to agronomic use of waste-derived phosphorus. [preprint]

Summary

Phosphorus (P) in animal manure, composts and waste products is frequently recycled on agricultural land, but evaluation and documentation of the fertiliser value of the P added with such highly variable sources is not straightforward. We assessed crop responses and responses in soil P test methods after application of solid town refuse composts, sewage sludge from wastewater treatment and diary cattle manure under field-like conditions on a low and a moderate P status soil. P concentration in the rye-grass crop was higher in the moderate P soil than in the low P soil. In both soils P concentration in the crop increased after P addition with all P sources in the first cut but not in the following three cuts. Manganese concentration in the plant tissue decreased in the treatments receiving compost or animal manure and it stayed low in all four cuts. This decrease was most probably caused by restricted manganese availability induced by the elevated soil pH measured in these treatments. Among the soil P tests the resin extraction, water extraction and the E1min could detect increases in available inorganic soil P pools in the treatments receiving P as composts, animal manure or NPK, while the Olsen P method failed to detect these changes. Treatments receiving P in iron or amuminum flocculated sewage slugde resulted in no or modest increases in soil P test values irrespective of the soil P test method. In contrast to this, the highest cumulated P offtake was measured after applying P as sewage sludge flocculated with iron. This study suggests that common soil P tests only partially reflects the P availability in soil amended with P from highly variable organic sources. Standardised characterisation of organic amendments and better information on how different groups of organic amendment may influence soil properties and processes are therefore needed.

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